What is it about?
In the past limits for the maximum permitted concentration of pollutant metals (e.g., copper, zinc, lead etc.) in surface water (stream, river, lake) were based on fixed concentrations that took no account of how that metal interacted with other chemical constituents in the water, nor considered the effect of multiple metals in the same water body. This has evolved somewhat so they currently consider availability of the metal for organism uptake by considering binding to a theoretical receptor based on a fish gill. However, this also fails to account for mixtures of different metals and how these interact with the water pH, which is acidic for many historical mine sites. This study defines a relationship between stream-water chemistry (considering major ions*, pollutant metals, pH and dissolved organic carbon) and the diversity of stream biology (in this case mayflies, caddisflies and stoneflies). *These are the things you see listed on a bottle of mineral water such as calcium, magnesium, sulfate, nitrate etc.
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Why is it important?
This study demonstrates that we can evaluate the potential ecological harm that exists from the entirety of the water chemistry. This allows a much more pragmatic approach to evaluation of water quality than looking only at single metals, where we may end up setting over-protective limits. This will enable regulators to better prioritise impacted systems for management and remediation.
Perspectives
As the regulatory environment evolves, we will require more data to develop models like these as they provide a robust site specific approach that should reduce the overprotective nature of fixed concentration regulatory limits. Nevertheless, more data is required for several metals that may be important in specific areas (for example lanthanides, silver, and several metals that form oxyanions)
Anthony Stockdale
Read the Original
This page is a summary of: Toxicity of proton–metal mixtures in the field: Linking stream macroinvertebrate species diversity to chemical speciation and bioavailability, Aquatic Toxicology, October 2010, Elsevier,
DOI: 10.1016/j.aquatox.2010.07.018.
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